Business, Basis of Presentation and Significant Accounting Policies - Adoption of New Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201802Member	us-gaap:AccountingStandardsUpdate201613Member
Unappropriated			$ (5,152)		$ (4,649)
Premium receivable and reinsurance recoverable, allowance for credit losses			19		0
Deferred policy acquisition costs and Value of business acquired			$ 1,669		2,226	$ 2,198	$ 2,973
Adoption of ASU
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs and Value of business acquired					$ 3
Retained Earnings (Deficit), Unappropriated | Adoption of ASU
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unappropriated				$ (33)
Mortgage loans on real estate | Adoption of ASU
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses				19
Reinsurance Recoverables | Adoption of ASU
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premium receivable and reinsurance recoverable, allowance for credit losses				28
deferred policy acquisition cost | Adoption of ASU
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs and Value of business acquired				5
Deferred Income Tax Charge | Adoption of ASU
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes				$ 9